The present invention relates to an ignition control device for an internal combustion engine, which is capable of cutting a current flowing through a primary side of an ignition coil without producing a spark in an ignition plug connected to a secondary side of the ignition coil.
An induction type ignition device which is widely used for the internal combustion engine employs an ignition coil having a primary winding and a secondary winding connected to an ignition plug so that, when an electric current flowing through the primary winding is cut off, a high voltage is induced across the secondary winding by which a spark discharge occurs across opposite electrodes of the ignition plug connected thereto.
The current flowing through the primary winding is on-off controlled usually by a semiconductor switching element. It becomes possible recently to control a time period for which the current flows through the primary winding and to regulate a value of the current flowing actually therethrough at a time when it is to be cut off to a certain level by means of electronics.
With the development of electronic engineering, an ignition control device by which a current flowing through the primary winding is made large enough to enable a high energy ignition has been realized.
In such ignition control device capable of using a large primary current, there is a defect that at a closure of a power switch or at a time when an engine stops to rotate such large primary current still remains in the primary winding, a value of which is still controlled by the ignition control device to a predetermined value, resulting in an over-heating and damage of the ignition coil and/or the control device.
In order to avoid such problem by cutting the primary current of the ignition coil off, an ignition energy is produced in the secondary side of the ignition coil by which an undesired spark is produced in the spark plug. If such spark occurs in a suction stroke of the engine, problems such as blowback of engine will occur.
Japanese Patent Application Laid-Open No. 18545/1977 discloses an ignition control device of analog type in which a primary current is reduced gradually when an engine stops to operate so that there is no such undesired spark. However, the proposed ignition control device uses a capacitor voltage to analog-control the primary current, together with a number of analog circuit elements. Therefore, an operation of the device is influenced largely by variations of these elements and tends to become unstable.